<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>吸顶容器</title>
  <style>
    .body {
      margin: 0px !important;
      padding: 0;
      box-sizing: border-box;
    }

    .road-tab-fixed {
      position: fixed;
      top: 0%;
      width: 100%;
    }

    .top {
      background: #c4f8b4;
      height: 50px;
    }

    .list {
      background: #ccc;
      width: 100%;
    }

    .list li {
      height: 50px;
      border-bottom: 2px solid #f00;
    }

    .banner {
      width: 100%;
      background: #c19aff;
      height: 150px;
    }
  </style>
</head>

<body>
  <div class="cont">
    <div class="banner">这是广告图</div>
    <div class="top" id="road-tab">菜单</div>
    <div class="list">
      <ul>
        <li>0</li>
        <li>1</li>
        <li>2</li>
        <li>3</li>
        <li>4</li>
        <li>5</li>
        <li>6</li>
        <li>7</li>
        <li>8</li>
        <li>9</li>
        <li>0</li>
        <li>1</li>
        <li>2</li>
        <li>3</li>
        <li>4</li>
        <li>5</li>
        <li>6</li>
        <li>7</li>
        <li>8</li>
        <li>9</li>
      </ul>
    </div>
  </div>
  <script src="https://cdn.bootcss.com/jquery/1.10.2/jquery.min.js"></script>
  <script>
    const fixedDom = $("#road-tab"),
      tabclass = "road-tab-fixed";
    let beforeElementScrollTop = 0;
    let beforeOffsetTop = fixedDom[0].offsetTop;
    //scroll节流
    const throttle = (func, wait, mustRun) => {
      var timeout,
        startTime = new Date();

      return function () {
        var context = this,
          args = arguments,
          curTime = new Date()
        clearTimeout(timeout)
        // 如果达到了规定的触发时间间隔，触发 handler
        if (curTime - startTime >= mustRun) {
          beforeElementScrollTop = document.documentElement.scrollTop
          console.log("beforelementScrollTop----------", document.body.scrollTop);
          func.apply(context, args);
          startTime = curTime
          // 没达到触发间隔，重新设定定时器
        } else {
          timeout = setTimeout(func, wait)
        }
      }
    }
    const winScroll = (e) => {
      const elementScrollTop = document.documentElement.scrollTop
      console.log('elementScrollTop--------------', elementScrollTop);
      if (beforeElementScrollTop - elementScrollTop <= 0) {//up
        console.log('up');
        if (beforeOffsetTop - elementScrollTop < 0) {
          fixedDom.addClass("road-tab-fixed")
        }
      } else {
        if (beforeOffsetTop - elementScrollTop >= 0) {
          console.log("UUUUUU");
          fixedDom.removeClass("road-tab-fixed")
        }
      }
    };
    $(window).off("scroll").on("scroll", throttle(winScroll, 10, 100));
  </script>
</body>
</html>